The present invention relates to the simulation of the engine braking, in particular on a vehicle powered by an electric motor, for example an electric vehicle and/or hybrid vehicle.
In a vehicle provided with at least one electric traction or propulsion motor, it is possible, in certain conditions, to use the electric motor as a generator and to thus obtain an electric braking means. Such a use is advantageous because, since it is regenerative, it makes it possible to recover some of the kinetic energy of the vehicle in order to recharge the batteries.
This electric braking may be engaged when the driver presses on the brake pedal and also when the driver lifts his foot from the acceleration pedal. In this last case, reference is made to deceleration without braking.
In particular, document FR2945243 describes a method for producing such an artificial engine brake when the acceleration pedal is not engaged. The torque applied is dependent in particular on the speed of the vehicle and the level of charge of the battery.
The majority of vehicles are provided with one or more active safety systems for avoiding undesirable behavior of the wheels. For example, a vehicle may comprise a wheel anti-lock system, such as ABS for example (anti-lock braking system from the German “AntiBlockerSystem”), and/or a wheel anti-skid system, such as an ESP (electronic stability program) system for example. These active safety systems communicate with one or more sensors able to provide information concerning the state of the wheels.
The active safety systems are set up so as to switch into a control state following certain detections by the sensor or the sensors.
For example, the active safety systems may be set up so as to transmit control signals in order to control hydraulic braking means, for example brake pads. For example, a wheel anti-lock system may transmit signals intended to loosen the brake pads so as to prevent the wheels from locking up. An anti-skid system may transmit signals intended to apply a hydraulic braking to one wheel or another so as to ensure the stability of the vehicle, in particular when turning.
The active safety systems may also be set up so as to transmit electronic signals intended for the engine. For example, a wheel anti-lock system may be set up so as to transmit torque requests to the engine so that the engine accelerates the rotation of the wheels. An anti-skid system may be set up so as to transmit requests to the engine intended to reduce the torque applied by the engine.
In conventional combustion vehicles, the level of engine braking is relatively low, such that this braking does not generally lead to a response of the active safety systems.
However, regenerative braking makes it possible to recover energy. Also, in the case of a vehicle provided with a regenerative braking means, it is beneficial to simulate the engine braking with a relatively increased braking level.
It has been proposed to integrate within the same vehicle an engine-braking simulation module able to develop simulated engine-braking instructions intended for the regenerative braking means, and one or more active safety systems, for example ABS and/or ESP.
It has been proposed to program the engine-braking simulation module such that it develops simulated engine-braking instruction values corresponding to relatively increased torque values in absolute terms. However, it is possible that these increased braking values could lead to a switching to a control state of one or more active safety systems.
The signals transmitted by the active safety system or the active safety systems could then prevail over the signals transmitted by the engine-braking simulation module. Since the engine-braking torque value is relatively increased, there is a risk, however, of relatively abrupt transitions during the switching from one state to the other of the active safety system or active safety systems. However, the directional stability of the vehicle is sensitive not only to the level of braking applied, but also to the variations of the braking applied. During returns to the normal state of the active safety system, the abrupt transitions of the applied torque thus risk leading to reactivations of the safety system to the control state.
There is thus a need for a method that would make it possible to avoid such oscillations, and more generally to combine energy recovery and safety.